Poly alpha-olefins comprise one class of hydrocarbon lubricants which has achieved importance in the lubricating oil market. These materials are typically produced by the polymerization of alpha-olefins typically ranging from 1-octene to 1-dodecene, with 1-decene being a preferred material, although polymers of lower olefins such as ethylene and propylene may also be used, including copolymers of ethylene with higher olefins. The poly alpha-olefin (PAO) products may be obtained with a wide range of viscosities varying from highly mobile fluids of about 2 cSt at 100° C. to higher molecular weight, viscous materials which have viscosities exceeding 100 cSt at 100° C. The PAO's may be produced by the polymerization of olefin feed in the presence of a catalyst such as AlCl3, BF3, or BF3 complexes. Subsequent to the polymerization, the lubricant range products may be hydrogenated in order to reduce the residual unsaturation. In the course of this reaction, the amount of unsaturation is generally reduced by greater than 90%.
The automotive industry is placing greater demands on engine oils—operating at higher temperatures for longer times; driving a demand for low viscosity PAO's, preferably 4 cSt, while desiring Noack volatility and low temperature performance properties. Thus, a need exists for low viscosity PAO's which exhibit low Noack volatility (ASTM D 5800 Standard Test Method for Evaporation Loss of Lubricating Oils by the Noack Method).
The properties of a particular grade of PAO are greatly dependent on the alpha-olefin used to make that product. In general, the higher the carbon number of the alpha-olefin, the lower the Noack volatility and the higher the pour point of the product. Conversely, the lower the carbon number of the alpha-olefin, the higher the Noack volatility and the lower the pour point of the product. For either olefin used, for automotive applications, the desired low Noack volatility and the lower pour point are generally conflicting goals for a PAO.
PAO's having a viscosity of 4 cSt are typically made from 1-decene and have a Noack volatility of 13-14% and pour point of <−60° C. PAO's having a viscosity of 6 cSt are typically prepared from 1-decene or a blend of alpha-olefins and have a Noack volatility of about 7.0% and pour point of about −60° C.